484 THE INTELLECTUAL RISE IN ELECTRICITY. 



be again attracted until, having touched some other body, 

 the acquired electricity is lost. This, which Von Guericke 

 saw, is now explained by Dufay. 



But Dufay went a little further and imagined a whirl, a 

 field of force, around the tube, and figured to himself the 

 action going on there and not in the body of the tube. 

 The attracted body, on touching the tube and becoming 

 electrified, acquires a field of its own, the two fields repel, 

 and so long as that of either body remains the same, the 

 relative position of the two is unchanged. But if the field 

 of the attracted feather, for example, is dissipated, the 

 feather falls back to the tube ; if the field of the tube is 

 varied, as it is by the hand moving from one end of the 

 tube to the other, then the feather swings to and fro, fol- 

 lowing the changes caused. 



It is while examining the repulsive action of the glass 

 tube that Dufay accidentally notes an effect which he says 

 u disconcerted me prodigiously ;" and well it might, for it 

 seemed to be subversive of every conclusion which he had 

 hitherto formed concerning the behavior of electrified 

 bodies. He is watching a bit of gold-leaf float in the air 

 under the repulsion of his excited glass tube. It occurs to 

 him to see what it will do when subjected to the action of 

 two electrified bodies ; and therefore he rubs a piece of 

 gum-copal and brings it to the leaf. To his utter astonish- 

 ment the leaf, instead of retreating from the electrified 

 gum, as it certainly did from the electrified glass, adheres 

 to it. He tries the experiment again and again, but in 

 every instance the leaf is drawn by the gum or by amber 

 or by Spanish wax, while it is repelled by the glass tube. 

 Yet a second glass tube or a piece of rock crystal brought 

 near the leaf exercises the same repelling effect as the orig- 

 inal tube. 



This was Dufay's most important discovery. "I cannot 

 doubt, " he says, "that glass and crystal operate in exactly 

 the opposite way to gum-copal and amber ; so that a leaf 

 repelled by the former because of the electricity which it 



